1. When the single-phase transformer is no-load, the current and the main magnetic flux are in different phases, and there is a phase angle difference aFe, because there is iron consumption current. The no-load current is a peaked waveform because of the large third harmonic.

2. AC current also flows in the armature winding of a DC motor. But the flow of its field winding is DC current. The excitation methods of DC motors include separate excitation, shunt excitation, series excitation, and compound excitation.

3. The expression of the back electromotive force of the DC motor is E = CE F n; and the expression of the electromagnetic torque is Tem = CTFI.

4. The number of parallel branches of DC motors is always in pairs. The number of parallel branches of the AC winding is not necessarily.

5. In a DC motor, the elements of a single stack winding are stacked one on top of the other and connected in series. Whether it is a single-wave winding or a single-stack winding, the commutator segments connect all elements in series to form a single closed loop.

6. The asynchronous motor is also called the induction motor, because the rotor current of the asynchronous motor is generated by electromagnetic induction.

7. When the asynchronous motor is started with reduced voltage, the starting torque decreases, and the starting torque decreases proportionally to the square of the starting current of the winding.

8. When the amplitude and frequency of the primary side voltage remain unchanged, the saturation degree of the iron core of the transformer is basically unchanged, and the excitation reactance is also basically unchanged.

9. The short-circuit characteristic of synchronous generator is a straight line, and the magnetic circuit is unsaturated when the three-phase symmetrical short-circuit occurs; when the three-phase symmetrical steady-state short-circuit occurs, the short-circuit circuit is a direct-axis component of pure demagnetization.

10. The current in the excitation winding of a synchronous motor is a direct current, and the excitation methods mainly include excitation generator excitation, static rectifier excitation, rotating rectifier excitation, etc.

11. There are no even-order harmonics in the three-phase composite magnetomotive force; symmetrical three-phase windings pass symmetrical three-phase currents, and there is no multiple of 3 magnetic harmonics in the composite magnetomotive force.

12. Three-phase transformers generally hope that one side is delta connected or the midpoint of one side is grounded. Because the winding connection of the three-phase transformer hopes to have the path of the third harmonic current.

13. When the symmetrical three-phase winding passes the symmetrical three-phase current, the 5th harmonic in the synthetic magnetomotive force is reversed; the 7th harmonic is forward.

14. The mechanical characteristics of series-excited DC motors are relatively soft. The mechanical characteristics of separately excited DC motors are relatively hard.

15. The transformer short-circuit test can measure the leakage impedance of the transformer winding; while the no-load test can measure the excitation impedance parameters of the winding.

16. The transformation ratio of the transformer is equal to the turns ratio of the primary winding to the secondary winding. The transformation ratio of a single-phase transformer can also be expressed as the ratio of the rated voltage of the primary and secondary sides.

17. During normal excitation, the power factor of the synchronous generator is equal to 1; keep the output active power unchanged, and make the excitation current smaller than the normal excitation (under-excitation), then the nature of the direct-axis armature reaction is magnetic-assisted; keep the output active power without When the excitation current is greater than the normal excitation (overexcitation), the nature of the direct axis armature reaction is demagnetization.

18. In a DC motor, the iron loss mainly exists in the rotor core (armature core), because the magnetic field of the stator core is basically unchanged.

19. In a DC motor, the first pitch y1 is equal to the number of slots between the first side and the second side of the component. The resultant pitch y is equal to the number of grooves that differ between the upper element sides of two elements connected in series.

20. In a DC motor, when saturation is not considered, the quadrature axis armature reaction is characterized by a position shift that makes the magnetic field zero, but the flux per pole is constant. When the brushes are on the geometric neutral line, the armature reaction is of an alternating magnetic nature.

21. In a DC motor, the component that converts the external DC power into the internal AC power is the commutator. The purpose of the commutator is to convert DC to AC (or vice versa).

22. In a synchronous motor, when the excitation flux F0 of the stator winding interlinkage is the maximum value, the counter electromotive force E0 reaches the minimum value, and when F0 reaches zero, E0 reaches the maximum value, and the phase between F0 and E0 The relationship is F0 ahead of E0 90o. And the relational expression between E0 and F0 is: E0 = 4.44 f N kN1F0.

23. In the motor, the leakage flux refers to the magnetic flux that only interlinks the winding itself, and the counter electromotive force generated by it can often be equivalent to a leakage reactance voltage drop (or negative reactance voltage drop).

24. There are two types of rotors for asynchronous motors: - squirrel cage type and winding type.

25. The slip s of the asynchronous motor is defined as the ratio of the difference between the synchronous speed and the rotor speed to the synchronous speed. When the asynchronous motor works in the motor state, the range of its slip s is 1>s>0.

26. The relationship between the electromagnetic torque Tem and the slip s of the asynchronous motor. =0). When the rotor resistance of the asynchronous motor changes, the characteristics of the size of the maximum electromagnetic torque Tem and the slip rate sm are: the size does not change, and the position of s changes.

27. The asynchronous motor must absorb lagging reactive power from the grid for excitation.

28. When a coil group is connected with alternating current, its magnetomotive force changes with time and has the property of pulse vibration. A single coil passes through alternating current, and its magnetomotive force also has the property of pulse vibration over time.

29. When the synchronous generator is connected to the grid, its three-phase terminal voltage is required to have the same characteristics as the three-phase voltage of the grid: frequency, amplitude, waveform, phase sequence (and phase), etc.

30. There are two types of rotors for synchronous motors: hidden pole type and salient pole type.

31. The number of equivalent phases of the squirrel cage rotor is equal to the number of slots, and the equivalent number of turns of each phase is 1/2.

32. Three-phase symmetrical AC windings, passing symmetrical three-phase alternating current, its fundamental synthetic magnetomotive force is a circular rotating magnetomotive force, and its direction of rotation is from the axis of the leading phase winding to the axis of the lagging phase, and then to the next Axis of a lagging phase.

33. There are two connection methods between the three-phase windings of the three-phase transformer, such as star and delta; the magnetic circuit has two structures, such as group type and core type.

34. The 6 odd-numbered connection group numbers of the three-phase transformer are 1, 3, 5, 7, 9, and 11. The 6 even-numbered connection group numbers are 0, 2, 4, 6, 8, and 10.

35. In the AC winding, the number of slots per pole and phase is q = q = Z/2p/m (assuming that the number of slots is Z, the number of pole pairs is p, and the number of phases is m). . In the AC winding, both 120o phase belt and 60o phase belt are used. Among them, the fundamental wave winding coefficient and the counter electromotive force of the 60° phase band are relatively high.

36. The symmetrical component method can be used to analyze the asymmetric operation of transformers and synchronous motors. The premise of its application is that the system is linear. Therefore, the principle of superposition can be applied to decompose the asymmetrical three-phase power system into positive sequence, negative sequence, Three sets of symmetrical three-phase systems such as zero sequence.

37. The calculation formula of the short-distance coefficient is ky1 = sin(p/2×y1/t), and its physical meaning is the discount (or reduction) of the counter electromotive force (or magnetomotive force) caused by the short distance compared with the full distance coefficient). The calculation formula of the distribution coefficient is kq1 = sin(qa1 /2 ) / q / sin(a1 / 2), and its physical meaning is that when q coils differ by a1 electrical angle in turn, the counter electromotive force (or magnetomotive force) is relatively concentrated The reduced coefficient (or discount) in the case of .

38. The current transformer is used to measure the current, and its secondary side cannot be open. The voltage transformer is used to measure voltage, and its secondary side cannot be short-circuited.

39. A motor is a device that converts mechanical energy into electrical energy (or vice versa), or changes one AC voltage level to another AC voltage level. From the perspective of energy conversion, motors can be divided into three categories: transformers, motors, and generators.

40. The formula for calculating the electrical angle a1 of the slot distance is a1 = p×360o/Z. It can be seen that the electrical angle a1 of the groove distance is equal to p times the mechanical angle am of the groove distance.

41. The principle of transformer winding reduction is: before and after the reduction, the magnetomotive force of the winding is guaranteed to remain unchanged, and the active and reactive power of the winding is guaranteed to remain unchanged.

42. The characteristic of the efficiency characteristic curve of the transformer is that there is a maximum value, that is, the maximum value is reached when the variable loss is equal to the constant loss.

43. The no-load test of the transformer usually applies voltage and measures on the low-voltage side. The short-circuit test of a transformer is usually applied and measured on the high-voltage side.

44. When the transformers are running in parallel, the conditions for no-load and no circulating current are: the same transformation ratio and the same connection group number.

45. When the transformers are running in parallel, the principle of load distribution is: the per unit value of the transformer load current is inversely proportional to the per unit value of the short circuit impedance. The conditions for the capacity of the transformers to be fully utilized during parallel operation are: the per-unit values of the short-circuit impedances must be equal, and their impedance angles must also be equal.